NOx adjustment system for gas turbine combustors

ABSTRACT

An embodiment may comprise a system for controlling NOx emissions from a turbine having combustion chambers. The system may comprise a center fuel flow and a plurality of outer fuel flows for each of a plurality of combustion chambers. An outer fuel flow is set to achieve a desired level of combustion dynamics for at least one of the plurality of combustion chambers. A delta adjustment value is determined for the center fuel flow that will result in a desired level of NOx emissions from the turbine, and for adjusting the center fuel flow according to the determined delta adjustment value to obtain the desired level of NOx emissions from the turbine.

BACKGROUND OF THE INVENTION

Current practice for NOx tuning of gas combustor turbines, used in powerplants for example, is to make incremental adjustments until a targetNOx emissions level is achieved. This process can be time consuming andrequires a technician to interrupt the normal operation of the gasturbine.

Gas turbines, typically have multiple combustion chambers. Thecombustion chambers are termed “cans” in the art. The can to canvariation in terms of fuel to air ratio leads to some cans being hotter,i.e. higher flame (or firing) temperature than others due to higher fuelto air ratio than other cans. These cans exhibit higher Nitrogen Oxides(NOx) emissions and certain pressure dynamic spectral tonescorresponding to higher flame temperature tend to be stronger. On theother hand, this variation can lead to one can burning very lean oralmost “blowing out” (i.e., flame extinguishes), if for example, thefuel to air ratio is below a certain threshold. The blowout of acombustion chamber or a can is termed “Lean Blow out” or LBO. Coldercans have higher LBO risk and higher Carbon Monoxide (CO) emissions dueto leaner fuel to air ratio than hotter cans that have higher NOxemissions due to higher fuel to air ratio. Colder cans also have certaindynamic tones that respond to colder firing temperature, i.e., tonesthat increase in amplitude as firing temperature decreases

Using pressure vibration sensors, feedback for each can, fuel flow andairflow is scheduled at the global or turbine level (total air and fuelfor all the cans) to meet turbine load requirements such that thecombustion dynamics in each can and emissions at the turbine level arewithin acceptable limits. Specifically, according to current combustiontuning practice, the overall fuel splits from the fuel system to thecans and the bulk fuel flow are set through the main fuel gas controlvalves.

However, an efficient method for tuning the f/a ratio in relation to NOxemissions is needed to ensure uniform life of the cans and to providemore efficient operation of the turbine and reduced emissions.

Thus, for example, in regard to NOx emissions a system that enablesadjustment of the fuel to air ratio of individual fuel valves in orderto meet defined NOx emission targets is needed.

BRIEF DESCRIPTION OF THE INVENTION

An embodiment may comprise a method or a system for controlling NOxemissions from a gas turbine having a fuel adjustment system that maycomprise setting an outer nozzle fuel flow to achieve a desired level ofcombustion dynamics for at least one of a plurality of combustionchambers; determining a delta adjustment value for a center nozzle fuelflow that will result in a desired level of NOx emissions from the gasturbine; and adjusting the center nozzle fuel flow according to thedetermined delta adjustment value to obtain the desired level of NOxemissions from the gas turbine.

An embodiment may also comprise a fuel adjustment system for controllingNOx emissions from a gas turbine having combustion chambers comprising:a center fuel nozzle and a plurality of outer fuel nozzles for each of aplurality of combustion chambers and a controller. The controller mayperform: setting an outer nozzle fuel flow to achieve a desired level ofcombustion dynamics for at least one of the plurality of combustionchambers; and determining a delta adjustment value for a center nozzlefuel flow that will result in a desired level of NOx emissions from thegas turbine; at least one first flow control device performing:adjusting the center nozzle fuel flow according to the determined deltaadjustment value to obtain the desired level of NOx emissions from thegas turbine; and at least one second flow control device performing:setting the outer nozzle fuel flow.

An embodiment may also comprise a system for controlling NOx emissionsfrom a turbine having combustion chambers comprising: a center fuel flowmeans and a plurality of outer fuel flow means for each of a pluralityof combustion chambers; means for setting an outer fuel flow means toachieve a desired level of combustion dynamics for at least one of theplurality of combustion chambers; means for determining a deltaadjustment value for the center fuel flow means that will result in adesired level of NOx emissions from the turbine, and for adjusting thecenter fuel flow means according to the determined delta adjustmentvalue to obtain the desired level of NOx emissions from the turbine.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions of various exemplary embodiments are notintended to be, and should not be considered to be, limiting in any way.

FIG. 1 is a diagram of a gas turbine having combustion cans.

FIG. 2 is schematic diagram of a typical combustor fuel system showingPM1 and PM3 fuel valves for example.

FIG. 3 is front view of an example of a fuel nozzle assembly showingPM1, PM2, PM3, fuel nozzles.

FIG. 4 is a data chart showing NOx input and output levels.

FIG. 5 is a screen shot of an example of a user interface.

DETAILED DESCRIPTION OF THE INVENTION

An example of a gas turbine is shown in FIG. 1. However, the presentinvention may be used with many different types of turbines, and thusthe turbine shown in FIG. 1 should not be considered limiting to thisdisclosure.

As shown in FIG. 1, a gas turbine 10 may have a combustion section 12located in a gas flow path between a compressor 14 and a turbine 16. Thecombustion section 12 may include an annular array of combustionchambers known herein as combustion cans 20. The turbine 10 is coupledto rotationally drive the compressor 14 and a power output drive shaft18. Air enters the gas turbine 10 and passes through the compressor 14.High pressure air from the compressor 14 enters the combustion section12 where it is mixed with fuel and burned. High energy combustion gasesexit the combustion section 12 to power the turbine 10, which, in turn,drives the compressor and the output power shaft 18. The combustiongases exit the turbine 16 through the exhaust duct 19, which may includea heat recapture section to apply exhaust heat to preheat the inlet airto the compressor.

Fuel is injected via the nozzles 24 into each chamber and mixes withcompressed air flowing from the compressor. A combustion reaction ofcompressed air and fuel occurs in each chamber. A more detaileddescription of one example of a fuel system is described in below inreference to FIG. 2; however other fuel systems are possible.

In FIG. 2 it can be seen that a main fuel valve 55 is located upstreamof four other valves. The four fuel to air ratio valves is this exampleare the Quat (Qt) valve 56, Premix 1 valve (PM1) 57, Premix 2 valve(PM2) 58, and Premix 3 valve (PM3) 59; however other arrangements arealso envisioned. In this example, a turbine having fourteen combustorcans is shown, but any number of combustor cans may be used dependingupon the application.

FIG. 3 shows the radial arrangement of the nozzles 24 in an exemplaryembodiment. In FIG. 3, there are three Premix 3 nozzles each labeledPM3. Likewise, there are two Premix 2 nozzles each labeled PM2. In thecenter, there is one premix 1 center nozzle (PM1). It is noted thatalthough a PM1 arrangement is used for purposes of example, thisinvention may be used with any center nozzle arrangement otherarrangements.

A direct method for changing NOx emissions based on targets or user setNOx emissions values did not previously exist. With the present methodone will be able to adjust directly from one NOx emissions level toanother using a transfer function that may be directly programmed into aturbine controller 61, for example or sent from a remote locationcontrol. See for example FIG. 4 wherein a current PM1 fuel split settingis shown at level 17 to result in a NOx output of 7. However, in FIG. 4,the user desires to have the NOx output be at level 8. Thus, in thisexample, the present method computes and/or determines a new PM1 settingof 17.45 to achieve the desired NOx output of level 8 as shown. FIG. 5is an example of a computer software interface that allows the user toenter the actual NOx that is sensed, and the system will adjust to a predefined NOx target.

Specifically, an exemplary embodiment of the present method and systemis described below in regard to a center nozzle gas turbine combustionsystems such as, but not limited to, the one shown in FIG. 3 forexample. Using a closed loop, the combustion system or gas turbine fuelsplits will be manipulated so as to match the actual emissions level ofthe gas turbine to a reference level. This reference level may bedetermined either by a transfer function or a direct reference levelentered by a user. One skilled in the art can use many suitable transferfunctions to achieve this result. This methodology will allow for NOxemissions changes that would be considered inside the normal acceptableadjustment range that is taken under consideration today by manualprocesses, and may be approximately +50% to −30% from design target, forexample. This method may also be programmed into gas turbine controllers61 for the purpose of offering a self-tuning (automatic adjustment tobounded reference) NOx emission control system, for example.

The method may be based on several combustor dynamics characteristics.For example, in one embodiment, the controller logic controls a logichierarchy of fuel flow so the entry fuel flow times the PM1 valve 57setting leaves a remainder amount of fuel. That remainder amount of fuelis split between the PM2 58 and PM3 59 valves (Quat (Qt) valve 56 may ormay not also be used). Therefore, adjustments to the PM1 fuel splitupstream automatically affect the PM3 fuel flow automatically because itis downstream in the hierarchy logic. Test data has shown that it isefficient to set the PM3 59 valve to achieve a desired combustorcombustion dynamic. For example, to achieve a setting where Lean BlowOut (LBO) does not occur, it is efficient to adjust the PM3 valve toachieve the desired combustor dynamic or operating state. For example, astate where a dynamic tone is present that indicates the desiredoperating state. Also, for example, Watts output may be regarded as anoperating state. Then, once the PM3 valve 59 is set, in the presentmethod, a suitable transfer function (not shown) is used to manipulatethe PM1 57 valve setting to achieve a desired NOx emissions level. Thus,in this embodiment the PM1 valve 57 setting is changed while the PM3valve 59 setting is held constant.

Benefits of the present method and system include but are not limited todecreasing time for a compliance cycle by automating the NOx emissionstuning process and maximizing the distance from LBO while maintainingacceptable emissions.

One of ordinary skill in the art can appreciate that a computer or otherclient or server device can be deployed as part of a computer network,or in a distributed computing environment. In this regard, the methods,systems, and apparatus described above and/or claimed herein pertain toany computer system having any number of memory or storage units, andany number of applications and processes occurring across any number ofstorage units or volumes, which may be used in connection with themethods and apparatus described above and/or claimed herein. Thus, thesame may apply to an environment with server computers and clientcomputers deployed in a network environment or distributed computingenvironment, having remote or local storage. The methods and apparatusdescribed above and/or claimed herein may also be applied to standalonecomputing devices, having programming language functionality,interpretation and execution capabilities for generating, receiving andtransmitting information in connection with remote or local services.

The methods and apparatus described above and/or claimed herein isoperational with numerous other general purpose or special purposecomputing system environments or configurations. Examples of well knowncomputing systems, environments, and/or configurations that may besuitable for use with the methods and apparatus described above and/orclaimed herein include, but are not limited to, personal computers,server computers, hand-held or laptop devices, multiprocessor systems,microprocessor-based systems, network PCs, minicomputers, mainframecomputers, distributed computing environments that include any of theabove systems or devices.

The methods described above and/or claimed herein may be described inthe general context of computer-executable instructions, such as programmodules, being executed by a computer. Program modules typically includeroutines, programs, objects, components, data structures, etc. thatperform particular tasks or implement particular abstract data types.Thus, the methods and apparatus described above and/or claimed hereinmay also be practiced in distributed computing environments such asbetween different power plants or different power generator units wheretasks are performed by remote processing devices that are linked througha communications network or other data transmission medium. In a typicaldistributed computing environment, program modules and routines or datamay be located in both local and remote computer storage media includingmemory storage devices. Distributed computing facilitates sharing ofcomputer resources and services by direct exchange between computingdevices and systems. These resources and services may include theexchange of information, cache storage, and disk storage for files.Distributed computing takes advantage of network connectivity, allowingclients to leverage their collective power to benefit the entireenterprise. In this regard, a variety of devices may have applications,objects or resources that may utilize the methods and apparatusdescribed above and/or claimed herein.

Computer programs implementing the method described above will commonlybe distributed to users on a distribution medium such as a CD-ROM. Theprogram could be copied to a hard disk or a similar intermediate storagemedium. When the programs are to be run, they will be loaded either fromtheir distribution medium or their intermediate storage medium into theexecution memory of the computer, thus configuring a computer to act inaccordance with the methods and apparatus described above.

The term “computer-readable medium” encompasses all distribution andstorage media, memory of a computer, and any other medium or devicecapable of storing for reading by a computer a computer programimplementing the method described above.

Thus, the various techniques described herein may be implemented inconnection with hardware or software or, where appropriate, with acombination of both. Thus, the methods and apparatus described aboveand/or claimed herein, or certain aspects or portions thereof, may takethe form of program code or instructions embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, or any othermachine-readable storage medium, wherein, when the program code isloaded into and executed by a machine, such as a computer, the machinebecomes an apparatus for practicing the methods and apparatus ofdescribed above and/or claimed herein. In the case of program codeexecution on programmable computers, the computing device will generallyinclude a processor, a storage medium readable by the processor, whichmay include volatile and non-volatile memory and/or storage elements, atleast one input device, and at least one output device. One or moreprograms that may utilize the techniques of the methods and apparatusdescribed above and/or claimed herein, e.g., through the use of a dataprocessing, may be implemented in a high level procedural or objectoriented programming language to communicate with a computer system.However, the program(s) can be implemented in assembly or machinelanguage, if desired. In any case, the language may be a compiled orinterpreted language, and combined with hardware implementations.

The methods and apparatus of described above and/or claimed herein mayalso be practiced via communications embodied in the form of programcode that is transmitted over some transmission medium, such as overelectrical wiring or cabling, through fiber optics, or via any otherform of transmission, wherein, when the program code is received andloaded into and executed by a machine, such as an EPROM, a gate array, aprogrammable logic device (PLD), a client computer, or a receivingmachine having the signal processing capabilities as described inexemplary embodiments above becomes an apparatus for practicing themethod described above and/or claimed herein. When implemented on ageneral-purpose processor, the program code combines with the processorto provide a unique apparatus that operates to invoke the functionalityof the methods and apparatus of described above and/or claimed herein.Further, any storage techniques used in connection with the methods andapparatus described above and/or claimed herein may invariably be acombination of hardware and software. The technical effect of theexecutable code is to facilitate the present methods of NOx emissionscontrol from a turbine.

While the methods and apparatus described above and/or claimed hereinhave been described in connection with the preferred embodiments and thefigures, it is to be understood that other similar embodiments may beused or modifications and additions may be made to the describedembodiment for performing the same function of the methods and apparatusdescribed above and/or claimed herein without deviating therefrom.Furthermore, it should be emphasized that a variety of computerplatforms, including handheld device operating systems and otherapplication specific operating systems are contemplated, especiallygiven the number of wireless networked devices in use.

While the invention is described with reference to the aboveembodiments, it is contemplated that the benefits of the inventionaccrue to alternative types and configurations. Consequently, thedescription set forth above is for illustrative purposes only, and isnot intended to restrict or limit the invention to any particularembodiment.

In addition, while the invention has been described with reference toexemplary embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another.

1. A fuel adjustment system for controlling NOx emissions from a gasturbine having combustion chambers comprising: a center fuel nozzle anda plurality of outer fuel nozzles for each of a plurality of combustionchambers; a controller structured to: set an outer nozzle fuel flow toachieve a desired level of combustion dynamics for at least one of theplurality of combustion chambers; and determine an adjustment value fora center nozzle fuel flow that will result in a desired level of NOxemissions from the gas turbine; at least one first flow control devicestructured to adjust the center nozzle fuel flow according to thedetermined adjustment value to obtain the desired level of NOx emissionsfrom the gas turbine; and at least one second flow control devicestructured to set the outer nozzles fuel flow.
 2. The system of claim 1wherein the at least one first flow control device is a premix valve. 3.The system of claim 1 wherein the at least one second flow controldevice is a premix valve.
 4. The system of claim 1 wherein the at leastone first flow control device is structured to adjust the center nozzlefuel flow while an outer nozzle fuel flows setting is held constant. 5.The system of claim 1 wherein the controller is structured to determinethe adjustment value for the center nozzle fuel flow that will result ina desired level of NOx emissions from the gas turbine by using atransfer function for determining the adjustment value for the centernozzle fuel flow to directly adjust the gas turbine from a first NOxemissions level to a second NOx emissions level.
 6. The system of claim5 wherein the transfer function is programmed into a turbine controller.7. The system of claim 5 wherein a result of the transfer function isdetermined at a remote location and transferred to a local turbinecontrol.
 8. The system of claim 1 wherein the controller is structuredto set the outer nozzle fuel flow to achieve the desired level ofcombustion dynamics for the at least one of a plurality of combustionchambers according to an operating state of the turbine.
 9. The systemof claim 8 wherein the operating state of the turbine is indicated bydynamic tones or watts output.
 10. A system for controlling NOxemissions from a turbine having combustion chambers comprising: a centerfuel flow means and a plurality of outer fuel flow means for each of aplurality of combustion chambers; means for setting an outer fuel flowmeans to achieve a desired level of combustion dynamics for at least oneof the plurality of combustion chambers; means for determining anadjustment value for the center fuel flow means that will result in adesired level of NOx emissions from the turbine, and for adjusting thecenter fuel flow means according to the determined adjustment value toobtain the desired level of NOx emissions from the turbine.
 11. Thesystem of claim 10 wherein the adjusting the center fuel flow means isperformed while an outer fuel flow means setting is held constant. 12.The system of claim 10 wherein the means for determining the adjustmentvalue for the center fuel flow means that will result in a desired levelof NOx emissions from the turbine further comprises: means for using atransfer function for determining the adjustment value for the centerfuel flow means to directly adjust the turbine from a first NOxemissions level to a second NOx emissions level.
 13. The system of claim10 wherein the means for setting the outer fuel flow means to achievethe desired level of combustion dynamics for the at least one of aplurality of combustion chambers is structured to perform according toan operating state of the turbine.